MOTIONALLY-INDUCED ELECTRIC AND MAGNETIC FIELDS OBSERVED IN THE IZU ISLANDS REGION

在伊豆群岛地区观测到的运动感应电场和磁场

• 批准号: 09440156
• 负责人: SASAI Yoichi
• 金额: $ 5.44万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1997
• 资助国家: 日本
• 起止时间: 1997 至 1999
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09440156/
• 关键词: Izu Islands sea region; Submarine cable electric field; geomagnetic observations; Island effect; Motionally-induced electric and magnetic field; Meander of Kuroshio current; Tide-induced magnetic field; BAYTAP-G; AFMT法比抵抗探査

We conducted observations of geomagnetic total force intensity on Miyake-jima, Kozu-shima. Mikura-jima and Hachijo-jima islands, electric field via ocean-bottom telephone cables among Izu-Oshima, Miyake-jima and Hachijo-jima islands, and long-distance self potential (SP), using telephone cables on Miyake-jima island. The observation is targeted at the behavior of EM fields induced by the dynamo action of conducting sea water under the main geomagnetic field in the oceanic area of southern Izu Islands region centered at Miyake-jima. In an open sea, no qontinl40us data are available to, monitor the overall distribution of ocean currents Instead of them, we presented a theoretical model of the tide in a flat ocean with a circular island and its, associated EM fields We also obtained the tidal constituents in the total intensity and ocean-bottom-cable electric field with the aid of the tidal analysis program BAYTAP-G. The model well explains the spatial dependence of the tide-induced total intensity on Miyake-jima By analogy, we inferred that the total intensity changes due to the meander of Kuroshio current should be mostly produced by electric currents in SE - NW direction, which was verified by the long-distance SP measurements across the island We carried out the resistivity soundings on Miyake-jima volcano by MT method. We found the low resistivity layer in the southern part of the island, where the amplitude of Kuroshio-induced magnetic field is large owing to the penetration of induced electric currents. A localized anomalous change was observed during the period from June 1996 to Sep. 1998, which suggests the thermal demagnetization within the volcano, i.e. the first observation of temperature rise since the 1983 eruption. The total intensity on Miyake-jima island has been slightly decreasing for the past 5 years, which is probably related to the inflation of the magma reservoir at depth through piezomagnetic effect.

我们在三宅岛、小津岛进行了地磁总力强度的观测。三仓岛和八丈岛、伊豆大岛、三宅岛和八丈岛之间海底电话电缆产生的电场以及三宅岛电话电缆产生的远距离自然电位（SP）。观测的对象是以三宅岛为中心的伊豆群岛南部海域的主地磁场作用下，海水导电发电机作用所产生的电磁场的行为。在远海中，没有140 μ s的资料来监测海流的总体分布。我们提出了一个具有圆形岛屿的平坦海洋中的潮汐及其相关电磁场的理论模型，并借助于潮汐分析程序BAYTAP-G得到了总强度和海底电缆电场中的潮汐分量。该模型较好地解释了三宅岛的潮汐总强度的空间依赖性。通过类比，我们推断黑潮弯曲引起的总强度变化主要是由SE-NW方向的电流引起的，并得到了长距离的自然电位测量的验证。在黑潮感生磁场幅值较大的岛屿南部，由于感生电流的穿透，发现了低阻层。在1996年6月至1998年9月期间观察到局部异常变化，这表明火山内部的热退磁，即自1983年爆发以来首次观察到温度上升。近5年来，三宅岛的总强度略有下降，这可能与压磁作用引起深部岩浆库的膨胀有关。

项目成果

渡辺 秀文: "伊豆大島火山1986年噴火の前兆過程とマグマ供給システム"火山. 43. 271-282 (1998)

Hidefumi Watanabe：“1986 年伊豆大岛火山喷发的前驱体过程和岩浆供应系统”火山。 43. 271-282 (1998)

UTSUGI, M., Y. NISHIDA, and Y. SASAI: "Piezomagnetic potentials due to an inclined retangular fault in a semi-infinite medium"Geophys. J. Int.. 140. 479-492 (2000)

UTSUGI, M.、Y. NISHIDA 和 Y. SASAI：“半无限介质中倾斜矩形断层引起的压磁势”地球物理学。

渡辺秀文: "伊豆大島火山1986年噴火の前兆過程とマグマ供給システム" 火山. 43・5. 271-282 (1998)

渡边秀文：“1986 年伊豆大岛火山喷发的前驱体过程和岩浆供应系统”，火山 43・5（1998 年）。

SASAI, Y. et al.: "Eletromagnetic minifouing of Miyabe-juma volcant, Igu-Brain Arc, Japan : A preliminary report."J. Germag. Geoelectr.. 49. 1293-1316 (1997)

SASAI, Y. 等人：“日本 Igu-Brain 弧 Miyabe-juma 火山的电磁微型爆炸：初步报告。”J.

UYESHIMA,M.,et al.: "Directional Properties of VAN's SES and ULFMT Signals at Ioanina,Greece" Phys.Earth Planet.Interiors. 105. 153-166 (1998)

UYESSHIMA,M.,et al.：“希腊约阿尼纳 VAN 的 SES 和 ULFMT 信号的方向特性”Phys.Earth Planet.Interiors。